### 1 OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION 

### UNITED STATES ENVIRONMENTAL PROTECTION AGENCY WASHINGTON, D.C. 20460

Date: November 27

, 2013 PC Codes: 031402, 031403, 031465 DP Barcode: D413486

MEMORANDUM

SUBJECT: Registration Review: Preliminary Problem Formulation for Environmental Fate, Ecological Risk, Endangered Species, and Drinking Water Exposure Assessments for 2,4

- DP

- p Containing R I somer Compounds (2,4

- DP

- p acid, 2,4

- DP

- p Amine salt, and 2,4

- DP

- p 2

- ethylhexyl ester)

FROM: Meghan Radtke , Ph.D., Biologist Faruque Khan , Ph.D., Senior Fate Scientist 

### Environmental Risk Branch I Environmental Fate and Effects Division ( 7507P)

REVIEWED BY: Michael Lowit, Ph.D., Biologist Stephen Wente, Ph.D., Biologist Environmental Risk Branch I Environmental Fate and Effects Division (7507P)

THROUGH: Sujatha Sankula , Ph.D., Branch Chief Monica Wait, Acting RAPL Environmental Risk Branch I Environmental Fate and Effects Division ( 7507P)

TO: Kaitlin Keller , Chemical Review Manager Tracy Perry, Team Leader Patricia Parrott, Branch Chief Risk Management and Implementation Branch III Pesticide Re

- Evaluation Division (7508P)

### 2 

## 1. Executive summary

The Environmental Fate and Effects Division (EFED) has completed the preliminary problem formulation for the ecological risk, environmental fate, endangered species, and drinking water assessments to be conducted as part of the registrat ion review of the herbicide propanoic acid, 2

- (2,4

- dichlorophenoxy)

- (R)

- ; propanoic acid, 2

- (2,4

- dichlorophenoxy)

- (R)

- comp ound with N

- methylmethanamine; and propanoic acid, 2

- (2,4

- dichlorophenoxy)

- (R)

- comp oun d with 2

- ethylhexyl ester. Abbreviated nam es for these chemicals are: 2,4

- DP

- p acid ; 2,4

- DP

- p dimethylamine (DMAS); and 2,4

- DP

- p 2

- ethylhexyl ester (EHE) , respectively

. From h ere forward, these compounds are referred to collectively as 2,4

- DP

- p and individually as acid, DMAS, and EHE

. The probl em formulation describes the methods planned to be used during the completion of drinking water and ecological r isk assessments in support of registration review and provide s an

ove rview of the environmental fate, ecological effects , and potential risks as sociated with the use of 2,4

- DP

- p as well as uncertain ties unique to risk assessment of 2,4

- DP

- p . This document also identifies additional studies that would be beneficial to the conduct of an ecological risk assessment. Major findings include:

• The fate database of 2,4

- DP

- p is partially complete

. EFED recommends the following studies be performed with the acid form : aerobic soil metabolism, anaerobic soil metabolism, anaerobic aquatic metabolism, fish bioaccumulation

, and environmental chemistr y methods (with independent laboratory validations).

• The ecotoxicity profile is partially complete

. EFED recommends the following studies : acute freshwater invertebrate (EHE), acute saltwater invertebrate (EHE and acid/ amine ), acute saltwater fish (EHE and a cid /amine ), chronic freshwater invertebrate ( a cid /amine ), chronic freshwater fish ( a cid /amine ), chronic saltwater fish ( a cid /amine ), chronic saltwater invertebrate ( a cid /amine ), acute avian oral (any compound) , avian reproduction (any compound) , honey bee larval toxicity (any compound )

, seedling emergence (ester

– soybean only ), and vegetative vigor ( a cid /amine ), vegetative vigor ( ester

– soybean only ). In the absence of this information, data from other phenoxy (2,4

- dichlorophenoxy) herbicides may be used , which may be more conservative

.

• The Agency has not received aquatic ecotoxicity studies for the major degradate, 2,4

- DCP. A search of the ECOTOX database indicates that some toxicity data may be available; these studies will be reviewed. If these s tudies are not considered valid for risk assessment purposes, conservative assumptions about 2,4

- DCP’s toxicity to aquatic organisms may be made using ECOSAR or other toxicity endpoint modeling tools. The Agency is interested in receiving any relevant, ex isting toxicity data for 2,4

- DCP.

• Some labels are missing information about the pounds of active ingredient applied on a per acre basis, number of applications per year, and minimum application interval. In the absence of this information, EFED will utili ze the use information that results in maximum exposure estimates for a given use pattern or make other conservative assumptions.

### 3 • A maximum application rate (on a per acre basis) should be identified for the spot
treatments. In the absence of this infor mation it will be assumed that no more than 1000 ft 2 

### are treated per acre

.

• For the granular formulations, the Agency will need to know the size of the granule and the amount of active ingredient contained within a granule. In the absence of this informati on, it may be assumed that birds and mammals could reasonably consume enough granules to induce an acute toxic effect.

• 2,4

- DP

- p is formula ted into a number of different products and may produce varied toxicological effects in plants, depending on the formu lation. Existing terrestrial plant toxicity data with different formulations would reduce that uncertainty. In the absence of data, the most protective toxicity values will be selected for terrestrial plant endpoints.



## 2. Introduction

There are active registrations for three different forms of 2,4

- DP

- p

– the acid form ( active ingredient ) and two other forms (one amine and an ester) that degrade in to the acid upon contact with the environment . The amine is an R isomer 2,4

- DP

- p amine sal t (DMAS ). The ester is 2,4

- D P

- p 2

- ethylhexyl ester ( EHE) and the acid is 2,4

- DP

- p acid (acid)

. Collectively, the three forms will be referred to as 2,4

- DP

- p. The structure of 2,4

- DP

- p , as well as the chemical names and other identifiers can be found in the chemical identity table ( Appendix A )

.
2,4

- DP

- p is a non

- systemic herbicide in the phenoxy or phenoxyacetic acid family. 2,4

- DP

- p causes disruption of auxin hormones in plants by affecting proteins in the plasma membrane, interfering with RNA producti on, and changing the properties and integrity of the plasma membrane. The plant's vascular system becomes blocked from excessive cell division and the resulting growth crushes the vascular transport system. Plant damage may include growth and reproductio n abnormalities, especially on new growth. Symptoms may appear on young growth almost immediately after application, but death may not occur for several weeks.

2,4

- DP

- p is primarily used on lawns, rights

- of

- ways, residential areas, and non

- cultivated agricultural land. According to the Biological and Economics Analysis Division (BEAD)

, an average of 8,000 lb a e/year of 2,4

- DP

- p was used on an annual basis from 2004 to 2010 in pastures

. 2,4

- DP

- p is used on < 1% to < 2.5% of the total pastureland in th e United States (USEPA, 2013 a ). According to technical and product labels, l iquid and granular applications are made using ground equipment; many are also made as spot treatments and stump treatments.

The most recent risk assessment of 2,4

- DP

- p was the E FED Re

- registration Eligibility D ocument Chapter (RED ; USEPA, 2007 a )

. It assessed the acid, DMAS (R enriched)

, and EHE forms. In this problem formulation, EFED considered the latest Agency science policies and risk assessment methodologies.

### 4 

## 3. Use Character ization

2,4

- DP

- p is a non

- systemic herbicide in the phenoxy or phenoxyacetic acid family that is applied post

- emergence to a wide variety of weeds

. It is registered for use on turf/lawns (commercial/industrial, residential, golf course, recreational, sod), airports/landing fields, outdoor household/domestic uses, non

- agricultural rights

- of

- way/fencerows/hedgerows,

non

- agricultural uncultivated areas/soils, fallow land, pastures, rangeland, paths and patios, paved areas, grasses grown for seed, forest t rees, and pine trees (USEPA, 2013b)

. It is not registered on any food /feed crops. 2,4

- DP

- p is formulated as a granule

, pressurized liquid, ready

- to

- use, soluble concentrate, and emulsifiable concentrate

. Treatment equipment include s spreader, sprayer, a tomizer type sprayer, controlled droplet applicator, low volume ground sprayer, spinning disc sprayer, drencher, trigger spray bottle, hose

- end sprayer, pump

- up sprayer, sprinkler can, tank

- type sprayer, high volume ground sprayer, product container, press ure sprayer, hand

- held sprayer, backpack
sprayer , tractor

- mounted sprayer, hand pressure sprayer, boom sprayer, compression sprayer, hand held spray wand, and power sprayer

.

The Screening Level Usage Analysis produced by BEAD (USEPA, 2013 a ) lists the use patterns of maximum exposure s for the current uses of 2,4

- DP

- p

. EFED will use application scenarios that result in maximum exposure scenarios for a given use for the risk assessment

. In the absence of information on the labels (e.g., maximum single

a pplication rate, the application interval, the annua l maximum rate allowed , rates in lbs

ae /year, application method s), EFED will utilize the use information that results in maximum exposure estimates for a given use pattern or make other conservative

assu mptions. Specifically, there are several uses for which this information is missing. In addition, some of the spot treatments result in application rates on a per acre basis that are very large . Revising the label to include a maximum yearly application rate (on a per acre basis) or providing additional information about the pounds of material expected to be used in an acre would allow for more realistic modeling of 2,4

- DP

- p spot treatment

uses. Please see Appendix B f or more details.



## 4. Conclusions from P revious Risk Assessments

a. Ecological Risk Assessment

The Agency only has one ecological risk assessment on 2,4

- DP

- p that serve s as a basis for this problem formulation document

– the EFED Chapter of the Reregistration Eligibility Decision ( USEPA, 2007a ) . The EFED RED chapter was conducted on the acid, DMAS (R enriched compound) , and EHE. The major degradate, 2,4

- DCP, was acknowledged in the RED, but not quantitatively incorporated into the assessment. The major ecological conclusions presented in the RED were as follows:

### 5 Table 1 . Summary of Risk Concerns Identified for 2,4

- DP

- p in the RED

Birds Mammals Terr

. Plants Terr

. Inverts Fish BCF Aquatic Inverts Aquatic Plants Groundwater Contam

. Persistence Degrad at es of Concern Yes b Yes b Yes NA c No No No Yes a No No Present d

a LOC only exceeded for one non

- vascular plant use (6 lb ae/A; aerial application of 2,4

- DP

- p DMAS).
b Chronic and acute risks were identified

. c No risks based on toxicity (hazard) classification. Yes = at least one LOC has been exc eeded in previous assessments; No = LOCs have not been exceeded in previous
assessments ; NA = RQs have not been calculated previously.
d 2,4

- DCP is a common degradate for many phenoxy herbicide s

. 

## b. **Drinking Water Exposure Assessments** 

EFED conducted an evaluation of concentrations of 2,4

- DP

- p to which humans may be exposed through the ingestion of drinking water (USEPA, 2007 b ). The assessment also included modeling and an evaluation of surface water and groundwater monitor ing data. A number of modeling scenarios were used to provide estimated drinking water concentrations (EDWCs) for drinking water

. Ground application on Christmas trees was the use produc ing the maximum estimated drinking water concentrations (EDWC) (US EPA, 2007b). EDWCs were 4 0. 2 μg/L (1

- in

- 10

- year peak ) and 2 .6 9 μg/L ( 3 0

- year mean) for surface water and 0.55 μg/L for ground water.



## c. **Clean Water Act Programs**

2,4

- DP

- p is not identified as a cause of impairment for any water bodies listed as impaired under section 303(d) of the Clean Water Act

. No Total Maximum Daily Load (TMDL) criteria have been developed for 2,4

- DP

- p and a quatic benchmarks have not been established ( http://www.epa.gov/oppefed1/ecorisk_ders/aquatic_life_benchmark.htm ) . Any data submitted or otherwise located as part of the registration review process may be used to update aquatic life benchmarks

, if applicable.


## 5. Environmental Fate and Transport

The physicochemical properties suggest that 2,4

- DP

- p acid is soluble in water (729 mg/L). The vapor pressure (1.28 × 10 - 6 

### mm Hg) and Henry's Law Constant (2.43 x 10 - 10



### atm

- m 3 

### /mol) indicate that the acid has a low volatility. The acid has low potential to bioaccumulate in aquatic organisms given the low value of the log n

- octanol/water partition coefficient (log K ow 

### 3.07). It is non

- persistent to moderately persistent and mobile in terrestrial and aquatic environments. Major routes of dissipation are pho todegradation in water ( DT 50 

### of 4 days) , microbial

- mediated degradation ( DT 50 s 

### of 14 to 34 days) , and leaching. 2,4

- DP

- p is stable to abiotic hydrolysis in pH 5, 7, and 9 buffer solutions. The pKa of 2

, 4DP

- p acid is 3.7 indicating that this compound will exist in an anion ic form (X

- COO

- H+) in the environment ( anions generally do not adsorb strongly to soils containing organic carbon and clay )

. Since the acid will be present primarily as an anion in soil at enviro nmental pH value s, there is a potential for both surface

### 6 runoff and leaching to groundwater. 

### Several field dissipation studies were performed for these chemicals ; they are currently under review.

2,4

- DP

- p formulations contain either the acid, DMAS

, or EHE

. 

### Given the rapid and

c omplete dissociation of DMAS and the rapid degradation of EHE in soil via microbial

mediated or surface catalyzed hydrolysis processes (DT 50 

### s of 12 to 24 hours) 

### leading to the formation of the acid, EFED employed an environmental fate bridging strategy of DMAS and EHE to the acid. T he one exception is exposure to the aquatic environment from the direct deposition from spray drift because EHE may persist in waters with an acidic to neutral pH. 

### The abiotic hydrolysis ranges from a DT 50 

### of 14 days in pH 9.0 to a DT 50 

### of 445 days in pH 5.0. T he exposure assessment for DMAS and EHE will be represented by the acid equivalent. The physical, chemical and environmental fate properties (of the acid)

a re presented in Table 2.

Table 2. Physical Chemical and Environmental Fate Properties of 2,4

- DP

- p Acid
Parameter Value Source Selected Physical/Chemical Parameters

Chemical Structure 1 TOXNET

IUAPC Name ( R )

- 2

- (2,4

- dichlorophenoxy)propionic acid MRID 47163502

CAS Name (2 R )

- 2

- (2,4

- dichlorophenoxy)propanoic acid MRID 47163502

CAS No. 15165

- 67

- 0 MRID 47163502 Molecular Weight (molecular formula) 235.07g/mol (C 9 H 8 Cl 2 O 3 ) U.S. EPA, 2005a
Smiles Code c1cc(Cl)cc(Cl)c1OC(C)C(=O)O EPISUITE 4.1 Vapor pressure (20°C) and (25°C) 6.22E

- 07 mbar (4.67E

- 07 mm Hg) @ (20°C) 1.70 E

- 06 mbar (1.28E

- 06 mm Hg) @ (25°C) MRID 437748

- 05

Aqueous solubility (20 ° C) 729 mg/L MRID 47163502

Dissociation constants (pKa ) in water (20°C) 3.67 MRID 438029

- 02

Henry’s Law Constant (25°C) 2.43E

- 10 atm

- m 3 /mol MRID 46591916 Log octanol

- to

- water partition coefficient (log K OW ) 3.07 MRID 438029

- 03

### 7 Parameter Value Source
Persistence Hydrolysis half

- life (25°C) 2,4

- DP

- p (acid) 2,4

- DP

- p (EHE) Stable 445 days at pH 5.0 3 12 days at pH 7.0 14 days at pH 9.0

Degradate 2,4

- DP

- p acid (76.2% of applied ) Unidentified Residue ( 6.1% of applied) MRID 426830

- 01 MRID 429176

- 01

Hydrolysis half

- life in Soil/Water system (25°C) Silty clay loam Sandy loam 12 hours 24 hours

Degradate s 2,4

- DP

- p acid (28.0% of applied ) 

### 4 chlorophenoxy

- propionic acid ( 4

- CPP; 2.0% of applied) Unidentified / unextractable ( 2.0% of applied) MRID 42937006

Aqueous photolysis half

- life (25°C) 4.0 days

Degradates 2,4 DCP (not quantified ) Unidentified degradates (>10% of applied) 1 MRID 43101501

Soil photolysis half

- life 12.15 days

Degradates 2,4 DCP (26.5% of applied) Unidentified degradate (4.1% of applied) MRID 42899601

Aerobic soil metabolism half

- life (days) Arkport soil

– 14.0 days

Degradates 2,4

- DCP (3.9% of applied) 2,4

- Dichloroanisole (DCA) (4.2% of applied) Unidentified degradate (2.8% of applied) MRID 42935301

Aerobic aquatic metabolism half

- life (total system) Krempe sediment/water

– 34.6 days Ohlau sediment/water

– 26.6 days

Degradates
CO 2 (79

- 90% of applied) MRID 42845806

Anaerobic aquatic metabolism half

- life (total system) No acceptable data

---

### 8 Parameter Value Source Mobility Adsorption/desorption

K d

- ads / K d

- des (mL/g)

K foc

- ads / K foc

- des (mL/g) Adsorption Freundlich adsorption K fads values Arkansas Clay

- 0.79 Georgia Sand

- 0.25 Sandy Loam 1.7 Timmerman sandy Loam 0.41

Desorption Freundlich adsorption K f

- des values Arkansas Clay

– 1.3 Georgia Sand

- 0.17 Sandy Loam 3.1 Timmerman sandy Loam 2.5

Adsorption Freundlich adsorption K foc values Arkan sas Clay

– 83.7 Georgia Sand

- 32.7 Sandy Loam

- 81.5 Timmerman sandy Loam

- 78.2

Desorption Freundlich adsorption K foc

- des values Arkansas Clay

– 143 Georgia Sand

- 21.9 Sandy Loam 149 Timmerman sandy Loam 474 MRID 44028901

Field Dissipation Terrestrial field dissipation half

- life Bare ground

- 4.2 days Turf

– 2.6 days MRID 44130103

Fish Bioconcentration

Fish bioconcentration factors (steady

state); depuration rate No data. ---

1 Structures and other physicochemical properties of various chemical forms can be obtained from Appendix A



## a. **Transformation Products**

The m a jor degradation product of 2,4

- DP

- p is 2,4

- dichlorophenol [ 2,4

- DCP (a common degradate for other phenoxy herbicides) , a maximum of 26.5% of applied] w as observed in environmental fate studies (Table 3)

. Recent problem formulations conducted for 2,4

- D (DP barcode 402410; 4/12/2013 2) , 2, 4

- DB
, and 2,4

- DB

- DMAS (DP barcod e

### 9 410362_Draft) detail the environmental fate properties of these compound s . Similar to these compound s , 2,4

- DP

- p is also primarily degraded through microbially

- mediated metabolism and photolysis forming 2,4

- DCP. Minor degradat ion products were 2,4

- dichloroanisol ( 2,4

- DCA ) (a maximum of 4.2%) in an aerobic soil metabolism study and unidentified c ompounds (maximum of 4.1%) in various environmental fate studies. Table 3 provides the transformation products of 2,4

- DP

- p and their maximum amounts formed

. 

### Table 3. Major Degradates of 2,4

- DP

- p Detected in Environmental Fate Studies
Code Name/ Synonym Chemical Name Chemical Structure Study Type Ref. (MRID) Maximum %AR (day)

2,4

- DCP 1 2,4

- dichlorophenol Soil photolysis 42899601 26.4 % ( 8 )

CO 2 Carbon dioxide Aerobic aquatic 42845806 90 % ( 92 )

1 A major degradate with toxicological significance and a common degradate for many phenoxy herbicides.


## 6. Receptors

Table 4 thr ough 6 provide a summary of the aquatic an d terrestrial taxonomic groups and the most sensitive surrogate species tested to characterize the potential acute and chronic ecological effects of 2,4

- DP

- p

. Given that the amine and acid forms of 2,4

- DP

- p are expected to differ from the ester for aquatic exposures, they will be considered separately here for aquatic organisms. T he ester form of 2,4

- DP

- p is expected to be more toxic to aquatic s pecies than the amines and acid , based on available fish toxicity data for 2,4

- DP

p and comparable aquatic data for other phenoxy herbicides

. In addition, the amine form immediately dissociate s into the acid whereas the ester does not; toxicity data from 2,4

- DP

- p and other phenoxy herbicides demonstrate similar endpoints for amines and acids. Assessing amine/acid forms separately from ester forms for aquatic exposures is consistent with other phenoxy herbicides.

For terrestrial species, all forms of 2 ,4

- DP

- p are expected to be equivalent in toxicity

, based on data from other phenoxy herbicides ; consequently, a pair of ester and acid/amine data are not required. The one exception is for terrestrial plants because the risk assessment has an aquatic comp onent (runoff). Consequently, plants are expected to be exposed to the ester form for a longer period of time than the amine, which immediately dissociates into the acid. Ecological studies with the major degradate, 2,4

- DCP, have not been submitted to th e Agency; however, a preliminary look at the open literature suggests it may be more toxic to some aquatic organisms than 2,4

- DP

- p

.

### 10 

## a. **Effects to Aquatic Organisms**

Table 4 . Summary of the Most Sensitive Endpoints from Aquatic Toxicity Studies for 2,4

- DP

- p A cid and Amines Taxonomic

Group Study Type Test Species and Chemical Toxicity Value (all units in terms of a cid equivalents ) Acute Toxicity Classification MRID

Freshwater fish 1 Acute Rainbow Trout ( Oncorhynchus mykiss )

– DMAS LC 50 > 91.5 mg

ae /L

No mortality Practically

non

- toxic 42767001

Freshwater invertebrates Acute Water Flea ( Daphnia magna )

- Acid EC 50 = 558 mg ae/L* Practically

non

- toxic 43867603

Chronic Water Flea ( Daphnia magna )

- Acid NOAEC = 100 mg ae/L LOAEC > 100 mg ae/L

No effects -- 46591903

Aquatic plants and algae Vascular Duckweed ( Lemna gibba )

- DMAS NOAEC = 1.8 7
mg ae /L EC 50 = 32 mg

ae /L

Based on reduction in number of fronds -- 46856701

Non

vascular Freshwater Diatom ( Navicula pelliculosa )

- DMAS NOAEC = 0. 0013 mg ae /L EC 50 = 0.077
mg ae /L

Based on cell density -- 42665701

1 Freshwater fish may be surrogates for aquatic

- phase amphibians. *Several tests with lower endpoints are available, but they yield “greater than” (non

- defin itive) values (ranged from > 82.3 to > 100 mg ae/L) , indicating that the EC 50 is higher than wh at was tested; there was no mortality. The cited study, although tested with a formulation, tested a wider range of doses and there is greater confidence that it has identified a value closer to the true EC 50 than the non

- definitive endpoint tests.



### Table 5 . Summary of the Most Sensitive Endpoints from Aquatic Toxicity Studies for 2,4

- DP

- p Este r Taxonomic

Group Study Type T est Species and Chemical Toxicity Value (all units in terms of ac id equivalents ) Acute Toxicity Classification MRID

Freshwater fish 1 Acute Bluegill sunfish ( Lepomis macrochirus )

– EHE LC 50 = 5.21 mg ae/L Moderately toxic 42767004

1 Freshwater fish may be surrogates for aquatic

- phase amphibians.

### 11 

## b. **Effects to Terrestrial Organisms**

Table 6 . Summary of the Most Sensitive Endpoints from Terrestrial Toxicity Studies for 2,4

- DP

- p

Taxonomic

Group Study Type Test Species and C h emical Toxicity Value (all units in terms of ac id equivalents ) Acute Toxicity Classification MRID

Birds 1 Acute Bobwhite quail ( Colinus virginianus )

- DMAS LD 50 = 242 mg

ae /kg

- bw Moderately toxic 42987901

Sub

- acute dietary Bobwhite quail ( Colinus virginianus )

- EHE LC 50 > 3804 mg

ae /kg

- diet

No mortality Practically

non

- toxic 43811401

Chronic Japanese quail ( Coturnix coturnix japonica )

- DMAS NOAEC = 244 mg ae/kg

- diet LOAEC = 732 mg ae/kg

- diet

Based on mortality and reduction in food consumption/weight gain -- 46879201

Mammals Acute Oral Laboratory rat ( Rattus norvegicus )

- DMAS LD 50 = 534 mg

ae /kg

- bw Slightly toxic 42614601

Acute Inhalation Laboratory rat (Acid) LC 50 >2.7 mg ae /L Toxicity Category IV 42985310

Chronic Laboratory rat ( Rattus norvegicus )

- Acid NOAEL = 40 mg ae/kg

- bw LOAEL = 219.6 mg

ae /kg

- bw

B ased on reduced body weight and food consumption -- 46721401

Insects Acute
contact Honey bee ( Apis mellifera L. )

- EHE LD 50 >17 μg ae/bee Practically

non

- toxic 42204601

Acute oral Honey bee ( Apis mellifera L. )

- Acid LD 50 > 1 00 μg ae/bee Practically

non

- toxic 46591910

Terrestrial plants Seedling Emergence (acid / amine) 2 Dicot

– lettuce ( Lactuca sativa )

- DMAS NOAEC = 0.0 05 lb ae/A EC 25 = 0.0083 lb ae/A

Based on dry weight -- 43016702

### 12 Taxonomic

Group Study Type Test Species and C h emical Toxicity Value (all units in terms of ac id equivalents ) Acute Toxicity Classification MRID

Monocot

– onion ( Allium cepa )

- DMAS EC 05 = 0.0 034 lb/A EC 25 = 0. 029 lb/A

Based on dry weight -- 43016702

Vegetative vigor (acid /

a mine) 2 Dicot

– cucumber ( Cucumis sativa )

- DMAS EC 05 = 0.00021 lb ae/A EC 25 = 0.0047 lb ae/A

Based on dry weight -- 43016701

Monocot

– onion ( Allium cepa )

- DMAS NOAEC <0.003 lb ae/A EC 25 = 0.014 lb ae/A

Based on dry weight -- 43016701

Seedling
emergence (ester) 2 Dicot

– oilseed rape ( Brassica
napus )

- EHE EC 05 = 0.00541 lb ae/A EC 25 = 0.0358 lb ae/A

Based on dry weight -- 47786303

Monocot

– onion ( Allium
cepa )

- EHE NOAEC = 0.0500 lb ae/A EC 25 = 0.078 lb ae/A

Based on dry weight -- 47786303

Vegetative vigor (ester) 2 Dicot

– oilseed rape ( Brassica
napus )

- EHE NOAEC = 0.0000686 lb ae/A EC 25 = 0.00139 lb ae/A

Based on dry weight -- 47786304

Monocot

– onion ( Allium
cepa )

- EHE NOAEC = 0.00186 lb ae/A EC 25 = 0.0162 lb ae/A

Based on dry weight -- 47786304

1 Birds represent surrogates for terrestrial

- phase amphibians and reptiles.
2 Ester and acid/amine values are listed for each terrestrial plant endpoint because separate assessments will be performed for the ester and acid/amine forms.



## c. **Ecological Incidents**

The ecological incident information system (EIIS) is an OPP database that houses ecological incidents that have been reported to the Agency. When available, EIIS

### 13 includes date and location of an incident, type and magnitude of effects observed in various species, use(s) of pesticides known or suspected of contributing to the incident, and results of any chemical residue analysis or other analyses conducted during incident investigation. EIIS incidents are categorized according to the certainty that the in cident resulted from pesticide exposure. The Avian Monitoring System (AIMS) is a database administered by the American Bird Conservancy that contains publicly available data on reported avian incidents involving pesticides. Many of the incidents listed i n this database are also in the EIIS

. The Aggregate Summary Module of OPP’s Incident Database was also consulted for reports of minor incidents to non

- target organisms.

EIIS returned one terrestrial plant incident in Indiana attributed to DMAS use with

“ possible” certainty (USEPA, 2007 a ) . Incident #I0 24272

- 225 occurred in June of 2012 when DMAS was applied in a residential area. Approximately 45% of the roses and ornamental plants in the vicinity were damaged

. As of August 29 , 201 3 , AIMS identified no ecological incidents involving 2,4

- DP

- p

.

R egistrants reported one minor wildlife incident and 867 minor plant incidents with 2,4

- DP

- p between 1995 and 2012 (aggregate incident database) . Unless additional information on these aggregated incidents becomes available, they will be assumed to be representative of registered uses of 2,4

- DP

- p in the risk assessment.



## 7. Exposure Pathways of Concern

The environmental fate properties and use patt erns of 2,4

- DP

- p indicate that direct spray, spray drift, leaching through soil (to groundwater or in subsurface lateral flow), and runoff represent potential transport mechanisms of 2,4

- DP

- p to non

- target aquatic and terrestrial organisms. Drinking water and inhalation exposure pathways were screened using the SIP (Screening Imbibition Program) and STIR (Screening Tool for Inhalation Risk) screening methods . Inhalation was found to be an e xposure pathway of low concern (no RQs are expected to exceed LOC s ) for mammals and birds ; however,
exposure concerns from the acid and amine forms (the ester form was not a concern) via drinking water are reasonably expected to occur for mammals and birds , given the results of the modeling . SIP and STIR are described i n detail at: http://www.epa.gov/oppefed1/models/terrestrial/index.htm and results are in Appendix C

. 

## 8. Analysis Plan

**a. Stressors of Concern** 

i. Ecological Risk Assessment

The stressors of ecological concern for terrestrial and aquatic organisms include the three forms of 2,4

- D P

- p . Submitted ecological studies indicate that the ester form for 2,4

- D P

- p is more acutely toxic to freshwater fish than DMAS , as holds true with ot her phenoxy

### 14 herbicides. Consequently, the ester will be considered separately for aquatic organisms

, as has been done in recent risk assessments (USEPA 2007 a ) . For terrestrial scenarios, the most sensitive endpoint, regardless of the 2,4

- D P

- p form (ester , amine, acid) will be used in the risk assessment. 2,4

- DCP is a maj or degradate in the terrestrial environment for all forms of 2,4

- DP

- p and t here are some toxicity data for 2

- DCP available in ECOTOX ( http://cfp ub.epa.gov/ecotox/ ) that suggest it is more toxic than 2,4

- D P

- p for some aquatic organisms. Pending results of reviewing the aquatic toxicity studies on the aquatic degradate 2,4

- DCP, this degradate will be included with 2 ,4

- DP

- p in the residues of concern modeled for aquatic exposure. Since, 2,4

- DCP may be more toxic than 2,4

- DP

- p for some aquati c species, aquatic exposures may be conduct ed for 2

, 4

- DP

- p and 2,4

- DCP separately or based on total equivalency factor (TEF) depending o n additional 2,4

- DCP data avai la bi lity

. In the absence of data, ECOSAR values may be used to predict the toxicity of 2,4

- DCP.

ii. Drinking Water

An EFED drinking water assessment w as conducted to support the RED human health risk assessment for 2,4

- DP

- p ( USEPA 2007 b ). If a revised drinking water assessment is warranted, EFED will conduct a drinking water assessment to support future human health dietary risk assessments of 2,4

- D P

- p . The drinking water assessment will be performed based on EFED’s current guidance using appropriate surface and groundwater models. Descriptions of all executable versions of current models for drinking water exposure can be obtained from URL link below. http://www.epa.gov/oppefed1/models/water/



## b. **Measures of Exposure**

EFED will use standard available models to evaluate potential exposures to aquatic and terrestrial organisms as described at http://www.epa.gov/pesticides/science/models_db.htm

. In addition, other available exposure models may be used to assess use in drains, drain lines, irrigation supply systems, waste water syst ems, sewage systems, sewer lines, and storm sewers , as applicable

.

i. Available Monitoring Data

The Agency is aware of monitoring conducted by federal and state agencies and this information will be considered in the assessment to the extent that data on 2,4

- DP

- p and its degradates are available.

### 15 

## c. **Measures of Effect**

Toxicity data presented in Section 3 of this problem formulation will be used to calculate risk quotients. Any additional information submitted by the registrant or found in the open literature prior to conduct of the risk assessment will also be consider ed. The open literature studies are identified using EPA’s ECOTOXicology database ( ECOTOX) (USEPA, 2007 c ), which employs a literature search engine for locating chemical toxicity data for aquatic life, terrestrial plants, and wildlife. The evaluation of both sources of data can also provide insight into the direct and indirect effects of pesticides on biotic communities from loss of species that are sensitive to the chemicals and from changes in structure and functional characteristics of the affected com munities.



## 9. **Endangered Species Assessments**

Consistent with the Agency’s responsibility under the Endangered Species Act (ESA), the Agency will eva luate risks to federally threatened and/or endangered (listed) species from registered uses of pesticides in re gistration review

. The process for evaluating potential risks to listed species is further described at http://www.epa.gov/oppfead1/endanger/litstatus/riskasses.htm

.



## 10. **Endocrine Dis ruptor Screening Program** 

2,4

- DP

- p was not included in the first or second group of chemicals issued /to be issued order s to conduct Tier 1 EDSP testing. For additional information the EDSP program, visit http://www.epa.gov/endo/

.


## 11. **Preliminary Identification of Data Gaps**

a. Environmental Fate

Table 7 identifies environmental fate studies by MRID that offer data for each guideline requirement, as well as study classifications and whether or not further da ta are needed in order to support risk assessment. Additional environmental fate data for 2,4

- DP

- p , as noted in Table 7

, will reduce uncertainty related to the exposure assessment.

### 16 Table 7

. Submitted Environmental Fate Data and Study Classifications for 2,4

- D P

p .

OCSPP Guideline Data Requirement Submitted Studies (MRID) Study Classifications Are data needed to conduct risk assessment? Justification and Assumptions EPA will Make in Absence of Data

835.2120 Hydrolysis 426830

- 01 Acceptable No

--

835.2240 Aqueous photolysis 43101501 Acceptable No

--

835.2410 Soil photolysis 42899601 Acceptable No

--

835.4100 Aerobic soil metabolism 42935301 Acceptable Yes

. Partially fulfilled

. Single aerobic soil metabolism study is acceptable for risk
assessment. Additional data for three soil s are required under 40 CFR Part 158 for terrestrial outdoor uses. OCSPP guidance recommends that these tests be performed with four soils. Given that OCSPP uses an upper 90 th percentile estimate of soil metaboli sm half

- lives based on available study data for modeling purposes, any additional data can reduce uncertainty related to the exposure assessment as well as the half

- life value used in modeling. Additional data are considered to have a high potential to add value to the ecological risk and drinking
water assessments.

835.4200 Anaerobic soil metabolism No data --

Yes D ata are required under 40 CFR Part 158 for terrestrial outdoor

uses. OCSPP guidance recommends that these tests be performed with four soils. Additional data are considered to have a low potential to add value to exposure assessments for the ecological risk and drinking water in presence of anaerobic aquatic metabolism ( 835.4400 )

.

### 17 OCSPP Guideline Data Requirement Submitted Studies (MRID) Study Classifications Are data needed to conduct risk assessment? Justification and Assumptions EPA will Make in Absence of Data

835.4300 Aerobic aquatic metabolism 42845806 Sup p lemental No

--

835.4400 Anaerobic aquatic metabolism No data.

-- Yes The assumption of compound stability will be made in the absence of acceptable data.

835.1230 835.1240 Adsorption/ desorption and leaching 44028901 Acceptable No

--

835.1410 Volatility

– laboratory No data.

-- No Not expected to be volatile under normal use conditions based on low vapor pressure and Henry’s Law Constant.

835.6100 Terrestrial field dissipation 44071401 44072402 44071403 44085501 44110801 44130101 44130102 44130103 44153701 4415 3702 44150703 44153704 TBD 1 TBD Registrant s submitted 1 2 terrestrial field dissipation studies

. A preliminary review suggests that these studies are scientifically sound

. Currently in review.

850.6100 Analytical method in soil No data. TBD TBD Currently in review

Analytical method in water No data.

-- Yes Environmental chemistry method (ECM) and independent laboratory validations (ILV) are required for 2,4DP

- p acid and its degradates

.

850.1730 Fish bioconcentration No data.

-- No 

### log K ow 

### 3.07 suggests low potential to bioaccumulate in aquatic organisms

1 

### TBD

- To be determined after final review of these studies

Environmental chemistry methods (ECM) for 2,4

- D P

- p residues of concern in water as well as independent laboratory validation (ILV) of the methods are required to support monitoring for 2,4

- D P

- p residues and to evaluate newly submitted environmental fate and ecological effects data. ILV methods submitted by the registrant are used to evaluate analyses described in submitted environmental fate and ecological effects studies. Submitted analytical methods are also used by various federal, state, tribal, and local

### 18 agencies to detect and moni tor residues that are or are suspected to be in environmental compartments from outdoor uses and accidental releases. Independent laboratory validations for submitted analytical methods are necessary to confirm that the methods are functional and to confi rm the levels of detection and quantitation reported in registrant

- prepared validations.



## b. Effects

Tables 8 and 9 i dentify ecological effects studies by MRID that offer data for each guideline requirement, as well as study classifications and whether or not further data are needed to support risk assessment. Although the ester form of 2,4

- DP

- p is more acutely toxic to freshwater fish, aquatic chronic studies are not requested given that it degrade s into the acid form ; the amines also rapidly dissociate into the acid form . Consequently, chronic exposure is only expected to occur with the acid form.

### 19 Table 8 . Submitted Aquatic Ecological Effects Data for 2,4

- DP

- p

OCSPP Guideline Data Requirement MRID (Compound) Study Classifications Are data needed to conduct

risk assessment? Justification and Assumptions EPA will Make in Absence of Data

850.1010 Freshwater invertebrate acute toxicity 43867603 ( Acid ) Acceptable Yes Data are needed for EHE because the ester form is generally more toxic to aquatic organism s than the acid / amine forms (based on other phenoxy herbicides and 2,4

- DP

- p freshwater fish dat a) . Without the submission of an acceptable study, data from 2,4

- DP

- p isooctyl ester may be used or a conservative estimate of the endpoint will be made based on data from other phenoxy herbicides

. 850.1025 850.1035 850.1045 850.1055

(Choice of four guidelines, but only one is needed to fulfill the requirement) Saltwater invertebrate acute toxicity (None) (N/A) Yes Data are needed for 1) a cid or amine; 2) EHE . Data are required for both the acid / amine and the ester because the ester form is
more to xic to aquatic organism s (based on other phenoxy herbicides and 2,4

- DP

- p freshwater fish data)

. Without the submission of acceptable studies

, conservative estimates of the endpoints will be made using data from other phenoxy herbicides (see the 2,4

- DP

- p R ED for examples)

. 850.1075 Freshwater fish acute toxicity 42767001 ( DMAS ) Acceptable No

--

40098001 ( EHE ) Acceptable

### 20 OCSPP Guideline Data Requirement MRID (Compound) Study Classifications Are data needed to conduct

risk assessment? Justification and Assumptions EPA will Make in Absence of Data

850.1075 Saltwater fish acute toxicity (None) (N/A) Yes Data are needed for 1) acid or amine; 2) EHE . Data are required for both the acid/amine and the ester because the ester form is more toxic to aquatic organism s (based on other phenoxy herbicides and 2,4

- DP

- p freshwater fish data)

. Without the submission of acceptable studies

, conservative estimate s of the endpoints will be made using data from other phenoxy herbicides (see the 2,4

- DP

- p RED for examples)

. 850.1300 Freshwater invertebrate life cycle 46591903 ( Acid ) Supplemental Yes The existing study did not measure growth endpoints, which are usually more sensitive than mortality endpoints. Thus, the study needs to be repeated with an acid or amine form of 2,4

- DP

- p. Without the submission of acceptable studies , conservative estimates of the endpoints will be made using data from other phenoxy herbicides (see the 2,4

- DP

- p RED for examples).

### 21 OCSPP Guideline Data Requirement MRID (Compound) Study Classifications Are data needed to conduct

risk assessment? Justification and Assumptions EPA will Make in Absence of Data

850.1350 Saltwater invertebrates life cycle (None) (N/A) Yes Data are needed for 2,4

- DP

p acid or amine

. Without the submission of an acceptable stud y , conservative estimates of the endpoints will be made using data from other phenoxy herbicides (see the 2,4

- DP

- p RED for examples).

850.1400 Freshwater fish early

- life stage (None) (N/A) Yes Data are needed for 2,4

- DP

p acid or amine ; t he study should be performed with the rainbow trout because this was the most sensitive species in the acute testing. Without the submission of an acceptable study

, conservative estimates of the endpoints will be made using data from other phenoxy herbici des (see the 2,4

- DP

- p RED for examples).

850.1400 Saltwater fish early

- life stage (None) (N/A) Yes Data are needed for 2,4

- DP

p acid or amine. Without the submission of an acceptable stud y , conservative estimates of the endpoints will be made using data from other phenoxy herbicides (see the 2,4

- DP

- p RED for examples).

850.1500 Fish life cycle (None) (N/A) No

-- 850.4400 Aquatic plant Toxicity Test using Lemna
spp. 4 6856701 ( DMAS ) Acceptable No Based on 2,4

- D data (a related phenoxy herbicide)

, the ester form of 2,4

- DP

- p is not expected to be more toxic to aquatic vascular plants than the acid/amine forms. Consequently data for the ester are not expected to yield a lower endpoint.

850.4500 Algal toxicity 42665701 ( DMAS ) Acceptable (freshwater diatom) Yes Data are needed for 2,4

- DP

p EHE for the freshwater diatom because the ester

### 22 OCSPP Guideline Data Requirement MRID (Compound) Study Classifications Are data needed to conduct

risk assessment? Justification and Assumptions EPA will Make in Absence of Data

42595902 ( DMAS ) Acceptable (green algae) Yes form is generally more toxic
to aquatic organism s than the acid/amine forms (based on other phenoxy herbicides and 2,4

- DP

- p freshwater fish data)

. Without the submission of acceptable studies , conservative estimates of the endpoints will be made using data from other phenoxy herbicides (see the 2,4

- DP

- p RED for examples). 42595901 ( DMAS ) Acceptable (marine diatom) Yes

850.4550 Cyanobacteria 42681001 ( DMAS ) Acceptable No A freshwater diatom study for EHE is being requested in lieu of cyanobacteria because freshwater diatoms were the most sensitive non

vascular aquatic plant to acid/amine forms for 2,4

- DP

- p.



### Table 9 . Submitted Terrestrial Ecological Effects Data for 2,4

- DP

- p

OCSPP Guideline Data Requirement MRID (Compound) Study Classifications Are data needed for risk assessment? Current Additional Data Need

850.2100 Avian oral toxicity 42987901 ( DMAS ) Acceptable Yes Data are required for one passerine species in addition to the northern bobwhite quail study that is already available (acid, amine, or ester)

. Without the submission of acceptable studies, conservative assumption will be made from the bobwhite quail study.

850.2200 Avian dietary toxicity 43811401 ( EHE ) Acceptable No

--

43220202 ( EHE ) Acceptable

### 23 OCSPP Guideline Data Requirement MRID (Compound) Study Classifications Are data needed for risk assessment? Current Additional Data Need

850.2300 Avian reproduction 468 79201 ( DMAS ) Supplemental Yes Data are required for one upland game species and one waterfowl species. The existing study is for the Japanese quail, which lays eggs continuously rather than cyclically, as seen in North American species. Consequently the data requirement for avian
rep roduction has not been
met. Without the submission of acceptable studies, conservative estimates of the endpoints will be made using data from other phenoxy herbicides (see the 2,4

- DP

- p RED for examples).

Non

guideline Avian inhalation (None) (N/A) No

--

850.3020 Honey bee
acute contact toxicity 42204601 ( EHE ) Acceptable No

--

OECD 213 Honey bee acute oral toxicity 46591910 ( Acid ) Supplemental No

--

OECD 237 Honey bee larval toxicity (None) (N/A) Yes Toxicity data for larval honeybees are necessary under the Pollinator White Paper (USEPA 2012). One study should be conducted with any 2,4

- DP

- p form.

850.3030 Honey bee residue on foliage (None) (N/A) No

--

850.3040 Field testing for pollinators (None) (N/A) No

--

850.4100 Seedling Emergence 43016702 ( DMAS ) Supplemental No

--

### 24 OCSPP Guideline Data Requirement MRID (Compound) Study Classifications Are data needed for risk assessment? Current Additional Data Need

and Seedling Growth 4 7786303 ( EHE ) Supplemental Yes Toxicity data for soybean with an ester is needed for the spray drift portion of the risk analysis. Without the submission of acceptable studies, conservative estimates of the endpoints
may be made using data from ot her phenoxy herbicides

. 850.4150 Vegetative Vigor 43016701 ( DMA S ) Supplemental Yes The existing NOAEC endpoint for the most sensitive plant ( onion) in the DMA S study yielded a non

definitive (less than) endpoint. A vegetative vigor study should be performed with onion using DMA S (racemic) . Without the submission of acceptable data, conservative estimates of the endpoints will be made using data from other phenoxy herbicides (see the 2,4

- DP

- p RED for examples)

or an I C 05 may be calculated

. 47786304 ( EHE ) Supplemental Yes Toxicity data for soybean with an ester is needed for the spray drift portion of the risk analysis. Without the submission of acceptable studies, conservativ e estimates of the endpoints
may be made using data from ot her phenoxy herbicides

.


### There are some toxicity data for 2 ,4

- DCP available in ECOTOX ( http://cfpub.epa.gov/ecotox/ ), which suggest it is more toxic th an 2,4

- D P

- p for selected aquatic organisms. There have been no registrant submitted environmental effects studies for this degradate , but the Agency notes that there are m ultiple freshwater invertebrate and fish studies for 2,4

- DCP in the ECOTOX database. The Agency plans to review these studies for the registration review risk assessment and incorporate toxicity information from this degradate, as appropriate. Some registrant

- submitted information is available for the environmental fate of 2,4

- DCP. The r egistrant and/or public is welcome to submit additional information that would validate 2,4

- DCP' s environmental fate and effects properties . In the case that the ECOTOX studies are not found to meet the Agency's criteria, conservative assumptions will be made about the fate properties

### 25 and t oxicological effects of 2,4

- DCP, including the use of predictive models to generate appropriate data

. T he Agency would be interested in any public perspective regarding the availability of data and its consistency with the Agency’s data evaluation criteria outlined in http://www.epa.gov/pesticides/science/efed/policy_guidance/team_authors/endangered_s pecies _reregistration_workgroup/esa_evaluation_open_literature.htm

Honeybee Larval Toxicity Test: Non

- Guideline Honeybee larval toxicity data are needed to complete a screening level risk assessment for risks to honeybees. In combination with acute contact toxicity and acute oral toxicity data, the larval toxicity component ensures that exposure routes to representative life stages of honeybees have been considered. The assessment process is further described in the Pollinator White Paper (USEPA 2012).



## 12. Ref erences

USEPA. 2007 a . Re

- registration eligibility document environmental fate and effects science chapter for 2,4

- DP

- p acid, 2,4

- DP

- p DMAS, and 2,4

- DP

- p EHE. Environmental Fate and Effects Division, Office of Pesticide Programs, U.S. Environmental Pr otection Agency. August 23, 2007 (D341297).

USEPA. 2007 b

. FQPA Drinking Water Assessment for Dichloroprop (2,4

- DP

- p)

. Environmental Fate and Effects Division, Office of Pesticide Programs, U.S. Environmental Protection Agency. April 12, 2007 (D322697)

. USEPA. 2012. White paper in support of the proposed risk assessment process for bees. Office of Chemical Safety and Pollution Prevention, United States Environmental Pr o tection Agency, Washington, DC. September 11, 2012.

USEPA. 2013 b . 2,4

- DP (031 416, 031419, 031463) screening level usage analysis. Biological and Economic Analysis Division, Office of Pesticide Programs, U.S. Environmental Protection Agency. January 30, 2013.

USEPA. 2013b. 2,4

- DP

- p Chemical Profile. Biological and Economic Analysis Division, Office of Pesticide Programs, U.S. Environmental Protection Agency. August 8, 13

### 26 

## Appendix A

. Selected physical and chemical properties of various forms of 2,4

- DP

- p

Table A. Selected Physical Chemical Properties of Various Forms of 2,4

- DP

- p PC Code Active Ingredient Molecular Formula and weight (g/mol) Structure , CAS # and CAS Name Solubility (mg/L) (Source) Dissociation constants (pKa ) in water Vapor Pressure (mm Hg@) and Source

031402 2,4

- DP

- p C 9 H 8 Cl 2 O 3 ( 235.06 )

CAS # 15165

- 67

- 0 (2 R )

- 2

- (2,4

- dichlorophenoxy)propanoic acid 729 ( Table 2 ) 3.67 1.28E

- 06 mm Hg (Table 2 )

031403 2,4

- DP

- p DMAS (R isomer compound) C 12 H 17 Cl 2 NO 5 ( 280.2 )

CAS # 104786

- 87

- 0 (2R)

- 2

- (2,4

- dichlorophenoxy) propanoic acid

- N

- methylmethanamine > 100 0000 MRID 427215

- 01 Mean pK a = 2.625 at 20.5°C R apidly dissociat ion at approximately 2 minutes MRID 427215

- 01 ≤ 2.55E

- 07 mm Hg (≤ 3.4 x 10 - 5
Pa ) MRID 427215

- 03

### 27 PC Code Active Ingredient Molecular Formula and weight (g/mol) Structure , CAS # and CAS Name Solubility (mg/L) (Source) Dissociation constants (pKa ) in water Vapor Pressure (mm Hg@) and Source

031465 2,4

- DP

- p EHE C 16 H 22 Cl 2 O 3 ( 347.3 )

CAS # 865363

- 39

- 9 2

- ethylhexyl (2 R )

- 2

- (2,4

- dichlorophenoxy)propanoate 170 MRID 440422

- 01 Not determined due to the very low solubility of the ester in water

(MRID 440422

- 01) 2 4.05 E

- 06 mm Hg ( 5.4 x 10 - 4 Pa at 20 ° C ) MRID 440422

- 08

P hysical and chemical properties of this compound assumed to be same as R enriched DMAS salt
2 2,4

– DP

- p 2

- EHE rapidly hydrolyze in soil slurries. The DT 50 of 2,4

- DP

- p 2

- EHE was < 12 hours and < 24 hours in slurries of acidic silty clay loam soil and slightly

- acidic sandy loam soil.

### 28 

## Appendi x B. Table of Uses and Application Rates (from USEPA , 2013b)

Use Method of Application Maximum Application Rate (in terms of a i* ) (minimum application interval) 2,4

- DP

- p acid Commercial/industrial lawns, golf course turf, ornamental lawns and turf, recreation area lawns, residential lawns Granular broadcast 2 apps per year at 0.364 lb ai/A (30 days)

Household/domestic dwellings outdoor treatment, nonagricultural rights

- of

way/fencerows/hedgerows, paths and patios, paved areas (private roads/sidewalks) Stump treatment 0.0568 lb /gal (as needed) 1,2

Household/domestic dwellings outdoor treatment, nonagricultural rights

- of

way/fencerows/hedgerows, paths and patios, paved areas (private roads/sidewalks) Foliar spray 0.0142 lb /gal (as needed) 1,2

2,4

- DP

- p DMAS
Commercial/industrial lawns, Granular broadcast 2 apps per year at 0.153 lb ai/A (30 days) Commercial/industrial lawns Granular broadcast 1 app per year at 1.79 lb ai/A Golf course turf Ground spray 1 app per year at 0.343 lb ai/A Grasses grown for seed Ground spray 2 apps per year at 0.286 lb ai/A (21 days) Nonagricultural rights

- of

way/fencerows/hedgerows Ground spray (spot treatment) 17.62 lb ai/A (30 days) 3
Nonagricultural uncultivated areas/soils Ground spray 1 app per year at 6.04 lb ai/A
Ornamental lawns and turf, ornamental sod farm/turf Ground spray (spot treatment) 2 apps per year at 59.9 lb ai/A (30 days)

Recreational areas Ground spray 2 apps per year at 0.335 lb ai/A (30 days)

Residential lawns Granular broadcast 2 apps per year at 0.465 lb ai/A (30 days)

Residential lawns Ground spray (spot treatment) 2 apps per year at 1.37 lb ai/A (30 days) 2,4

- DP

- p EHE Agricultural uncultivated areas Stump treatment 1 app per year at 1.52 lb/23 gal 1 Agricultural uncultivated areas Ground spray 1 app per year at 2.91 lb ai/A

### 29 Use Method of Application Maximum Application Rate (in terms of a i* ) (minimum application interval) Airports/landing fields, commercial/industrial lawns, commercial/institutional/industrial premises/equipment, golf course turf, household/domestic dwellings (outdoor premises), nonagricultural rights

- of

way/fencerow/hedgerow, pave areas (private roads/sidewalks), recreation area lawns, residential lawns Ground spray 2 apps per year at 0.531 lb ai/A (30 days)

Forest trees, ornamental lawns and turf, ornamental sod farm (turf), pine (forest/shelterbelt) Spot treatment 2 apps per year at 2.94 lb ai/A (30 days) Nonagricultural uncultivated areas/soils Basal bark treatment 1 app per year at 5.08 lb/1.3 gal 1
Nonagricultural uncultivated areas/soils Foliar treatment 3.25 2 lb ai/A

* Rates on the label report from BEAD were reported in active ingredient (ai) rather than acid equivalents (ae) (USEPA, 2013b)
1 Rate needs to be reported in lbs ai/A rather than in lbs ai/gal
2 Number of applications and application interval is missing
3 Number of applications is missing

### 30 

## Appendix C

. Screening Level Models to Evaluate Potential Importance of Drinking Water and Inhalation Exposure Pathways

SIP ( Screening Imbibition Program, v1.0) was used to calculate an upper bound estimate of 2,4

- DP

- p exposure via drinking water using solubility of 2,4

- D P

- p acid (729 mg/L) and EHE (170 mg/L) , the most sensitive acute and chronic avian toxicity endpoints (bobwhite quail, LD 50 

### = 2 42 mg ae /kg

- bw ; Japanese quail NOAEC > 244 mg ae/kg

- diet) and the most sensitive acute and chronic mammalian toxicity endpoints (rat LD 50 

### = 534
mg ae /kg

- bw and NOAEL = 40 mg ae /kg

- bw). The model indicated that there are acute and chronic concerns to birds and mammal s through the drinking water exposure pathway for the acid and amine forms (the amine form is represented by the acid)

. There are no concerns to birds and mammals from the ester form. Results for 2,4

- DP

- p acid are presented in Tables B.1 and B.2

.

Table B.1. SIP Mammalian Results for 2,4

- DP

- p
Parameter Acute Chronic Upper bound exposure (mg/kg

- bw) 125.3880 125.3880 Adjusted toxicity value (mg/kg

- bw) 410.7317 30.7664 Ratio of exposure to acute toxicity 0.3053 4.0755

Conclusion* Exposure through drinking water alone is a potential

concern for mammals Exposure through drinking water alone is a potential

concern for mammals



### Table B.2. SIP Avian Results for 2,4

- DP

- p
Parameter Acute Chronic Upper bound exposure (mg/kg

- bw) 590.4900 590.4900 Adjusted toxicity value (mg/kg

- bw) 174.3439 31.8300 Ratio of exposure to toxicity 3.3869 18.5514

Conclusion* Exposure through drinking water alone is a potential concern for birds Exposure through drinking water alone is a potential concern for birds *Conclusion is for drinking water exposure alone. This does not combine all routes of exposure. Therefore, when aggregated with other routes ( i.e. , diet, inhalation, dermal), pesticide exposure through drinking water may contribute to a total exposure that has the potential for additional effects to non

- target animals.



### STIR ( S creening T ool for I nhalation R isk, v1.0) was used to calculate an upper bound estimate of 2,4

- D P

- p exp osure via inhalation using 2,4

- D P

- p’s (acid) molecular weight (235.07 g/mole), vapor pressure (1.28 x 10 - 6 

### mmHg), high end application rate (5.08 lb ae/A), most sensitive acute avian toxicity endpoint (bobwhite quail, LD 50 

### = 242 mg

ae /kg

- bw), and most sens itive acute oral and inhalation mammalian toxicity endpoints (rat, LD 50 

### = 534 mg ae /kg

- bw and 4 hr LC 50 

### > 2.7 mg ae /L, respectively). Inhalation alone is not a potential pathway of concern for birds (droplet inhalation) for 2,4

- D P

- p acid (Table B.3); expo sure is not likely significant for birds. The results for mammals also indicated no adverse effects from the inhalation exposure route (Table B.4 ). Exposure is not likely significant for mammals.

### 31 Table B.3. STIR Avian (0.020 kg) Results for 2,4

- DP

- p Acid Maximum Vapor Concentration in Air at Saturation (mg/m 3 ) 1.62E

- 02 Maximum 1

- hour Vapor Inhalation Dose (mg/kg) 2.04E

- 03

Adjusted Inhalation LD 50 6.82E+0 0

Ratio of Vapor Dose to Adjusted Inhalation LD 50 2.98E

- 04 Exposure not Likely Significant

Maximum Post

- treatment Spray Inhalation Dose (mg/kg) 5.37E

- 01 Ratio of Droplet Inhalation Dose to Adjusted Inhalation LD50 7.87E

- 02 Exposure not Likely Significant

Table B.4. STIR Mammalian (0.15 kg) Results for 2,4

- DP

- p Acid Maximum Vapor Concentration in Air at Saturation (mg/m 3 ) 1.62E

- 02 Maximum 1

- hour Vapor Inhalation Dose (mg/kg) 2.56E

- 03 Adjusted Inhalation LD 50 1.61E+02

Ratio of Vapor Dose to Adjusted Inhalation LD 50 1.59E

- 05 Exposure not Likely Significant Maximum Post

- treatment Spray Inhalation Dose (mg/kg) 6.75E

- 01 Ratio of Droplet Inhalation Dose to Adjusted Inhalation LD50 4.20E

- 03 Exposure not Likely Significant